The invention relates to bottle closures, and more particularly to bottle closures designed to relieve excess internal bottle pressure.
The type of closure to which this invention relates is shown in Osborne et al U.S. Pat No. 3,303,955. Such a closure preferably employs screw threads to engage the neck of a bottle and utilizes both top and side sealing areas to withstand internal bottle pressures in excess of 240 p.s.i. The top seal is formed along a flat annular horizontal finish at the top of the bottle, and the side seal is formed along a usually vertical cylindrical finish of the bottle just below and outside the top finish. A disc or ring-shaped resilient sealing liner is engaged between the top of the closure and top finish of the bottle and between the cylindrical side skirt of the closure and the side finish of the bottle to form the top and side sealing areas. The closure is formed in situ on the bottle from a generally cylindrical cap blank having no threads and including a resilient sealing liner disc or ring positioned therein. A capping machine forces the cap blank downwardly on the bottle, bending a peripheral portion of what was originally the top panel of the cap blank downwardly to form a cylindrical portion of the side skirt, somewhat smaller in diameter than the remainder of the skirt. After this operation, which forms the top and side seals of the bottle closure, has taken place, a thread roller deforms the lower portions of the skirt of the cap blank into conformity with the threads of the bottle.
Although such a bottle closure includes both top and side sealing areas, it is the side seal which is stronger and enables the closure to withstand more than 240 p.s.i. internal bottle pressure. Under high pressures, the top panel of the closure is able to bulge upwardly to a degree sufficient to allow pressurized gas to pass into the top sealing area. However, the cylindrical side seal is more difficult to push outwardly sufficiently to allow the escape of gas therethrough.
In a high pressure vessel such as a sealed bottle containing a carbonated beverage, there is a need for some means of relieving excess pressure which may develop under extreme conditions. For example, in the shipping and storage of bottles of carbonated beverages high temperatures are often encountered. These temperatures are sometimes sufficient to raise the pressure within the bottle high enough to cause failure of a glass bottle. Such bottle failure pressure is generally well below the maximum pressure capability of the closure.
U.S. Pat. No. 2,032,931 shows a venting bottle closure having arcuate relieved portions extending downward from its top surface for engaging a resilient sealing liner between the relieved portions and the top bottle finish. Between adjacent relieved portions of the closure are areas which are not relieved, permitting the sealing liner to arc upwardly in those areas under internal gas pressure to allow a portion of the gas to escape. The bottle and closure shown in this patent do not employ a side seal. U.S. Pat. No. 2,138,376 shows another venting bottle closure of the top seal type similar to that of the above patent, but requiring a modified bottle finish for permitting high pressure gas to escape. U.S. Pat. No. 3,713,545 shows a closure of the top and side seal type including pressure relieving means. The relief feature of this closure relies upon a rupturable score line in the top panel of the closure, which ruptures under high pressure to open a slit and allow the resilient liner to balloon outwardly. This is stated to draw liner material away from the side and top sealing surfaces, thereby allowing gases to pass through the seals.
Additional venting closures are shown in U.S. Pat. Nos. 2,789,719 and 3,005,455.
Prior art venting bottle closures do not provide an effective side seal release for relieving excess gas pressure above a safe, relatively low predetermined magnitude which may be, for example, between about 80 and 150 p.s.i. In particular, an effective side seal relieving closure has not been provided on the type of container closure shown in Osborne et al Patent No. 3,303,955 discussed above. In addition, many previous venting closures have not been resealable after a venting has occurred.